1. Field of the Invention
The present invention relates to a key pattern connecting device for a domed metal switch, and more particularly to a key pattern connecting device for a domed metal switch having connection patterns provided to a main board and a flexible circuit, respectively, in such a manner that the main board and the flexible circuit are electrically connected to each other without an auxiliary key connecting part on the domed metal switch.
2. Description of the Related Art
Generally, “a mobile communication device” means a device that is portable and enables an owner of the device to communicate in a wireless way. Such a mobile communication device includes, for example, a bar-type wireless communication terminal comprising a single housing; a flip-type wireless communication terminal comprising a bar-type housing and a flip part pivotably attached to the housing; and a folder-type wireless communication terminal comprising a bar-type housing and a folder part pivotably attached to the housing. The aforesaid conventional mobile communication devices essentially include an antenna, data input/output units, and data transmitting/receiving units. Usually, the data input unit is a keypad that is pressed down to input data. Alternatively, a touch pad or a touch screen may be used. The keypad, which is used to input data, basically comprises an array of several keys. The keys include, for example, a send key (SND), which is a communication start key, a cancel key, a clear key (CLR), numeric keys, letter keys, an end key (END), functional keys, and a power on/off key (PWR).
The aforesaid keys are usually arranged on the surface of the housing of the mobile communication device up to the number of about 15 to 20. Of course, the keys are exposed on the surface of the housing to enable a user to input desired data by pressing down on the keys using his/her finger. The keys of the mobile communication device may comprise a domed metal switch, which enables the user to actually feel that he or she is operating the communication device.
As illustrated in FIG. 1, the domed metal switch includes a main body 1, on which a main board 2 is provided with a plurality of first and second contact parts 2a and 2b arranged in a key matrix. Domed metal keys 3 are arranged on the first and the second contact parts 2a and 2b. 
As illustrated in FIG. 2, around the domed metal keys 3 is provided a first adhesive 4, which fixes the key to the main board 2. On the first adhesive 4 is attached a light diffusion film 5, which is also provided around the domed metal keys 3. On the surfaces of the light diffusion film 5 and the domed metal key 3 are applied a second adhesive 6, to which a transparent film 7 is attached. The domed metal keys 3 include a plurality of main keys 3a and auxiliary keys 3b, such a volume key, as illustrated in FIG. 4.
As illustrated in FIGS. 3 and 4, the main keys 3a and auxiliary keys 3b, being 16 in number, are arranged in a key matrix of 4×4. On the main board 2 are provided a plurality of main connection patterns 9 in such a manner that the first contact parts 2a are electrically connected to Row0, Row1, Row2, and Row3, respectively. Similarly, on the main board 2 are provided a plurality of main connection patterns 9 in such a manner that the second contact parts 2b are electrically connected to Col0, Col1, Col2, and Col3, respectively. The Rows and Cols together form a key input controller 20. The auxiliary keys 3b, which are provided at one side of the main board 2, are electrically connected to the main board 2 by means of an auxiliary key connecting part 8 provided separately on the main board 2. The auxiliary key connecting part 8 may be formed of a flexible connector or a solder connector. The auxiliary keys 3b include a flexible circuit 10, on which first and second contact parts 11 and 12 are provided.
Connection patterns 13 are further provided on the flexible circuit 10 in such a manner that the first contact parts 11 are electrically connected to Row2 and Row3, respectively, and the second contact parts 12 are electrically connected to Col3, while the first and second contact parts 11 and 12 of the auxiliary keys 3b are connected to the auxiliary key connecting part 8. The domed metal keys 3 are provided on the first and second contact parts 11 and 12 connected as mentioned above. At this time, prior to a user pressing on the keys, the domed metal keys 3 come into contact with the first contact parts 2a, not the second contact parts 2b provided in the first contact parts 2a. 
The operation of the domed metal keys 3 arranged in a key matrix will now be described with reference to FIG. 5. Prior to the keys being pressed down in the key matrix (initial condition), all bits in an internal 10-bit register are ‘0.’ That is, the resulting value output from the key matrix is ‘00000 00000.’ At this time, when a user presses down the key at Row0 and Col0 on the key matrix, i.e., key[0][0], there occurs a key interrupt, and the resulting value of the interrupt displayed on the internal 10-bit register of the controller of the mobile communication device will be ‘00001 00001.’ Then, in order to confirm that the key at Row0 and Col0, i.e., key[0][0], has been pressed down, the key input controller divides the internal 10-bit register into upper 5 bits and lower 5 bits, and checks which of the bits is ‘1,’ respectively. As a result, it is confirmed that the pressed key is key[0][0], which is in turn compared to the previous pressed key. Since no key is previously pressed down, it is recognized that the present pressed key is key[0][0]. Under this condition, if the user presses down key[1][1], the resulting value of the key interrupt displayed on the internal 10-bit register by the key interrupt from the key matrix will be ‘00011 00011.’ At this time, the internal 10-bit register is divided into upper 5 bits and lower 5 bits, and it is checked which of the bits is ‘1,’ respectively. Expected keys from the key input controller are key[0][0], key[0][1], key[1][0], key[1][1] . . . Since key[0][0] was previously pressed down and key[1][1] is presently pressed down, the key input controller determines logically the state of the previous and present keys to determine that the present pressed key is key[1][1] among key[0][0], key[0][1], key[1][0], key[1][1] . . .
Since the aforesaid conventional domed metal switch further includes the auxiliary key connecting part for connecting the auxiliary keys to the main board, however, there is further needed space for the auxiliary key connecting part on the main board, which makes it difficult to reduce the size and weight of the mobile communication device. Furthermore, since the auxiliary key connecting part of the conventional domed metal switch is made of a flexible connector or a solder connector, there is further needed a step for soldering the connector to the main board, which may increase the potential for defective products. As a result, reliability of the products becomes reduced, a process for assembling the products is complicated, and the costs for manufacturing the products are increased. In addition, static electricity is applied frequently to the domed metal switch via the key parts of the switch. However, as the size of the mobile communication device is reduced, a part for discharging the static electricity becomes weaker. Consequently, the main board may not be stable because of the static electricity. In cases where static electricity is applied to the main board via the keys of the domed metal switch, the static electricity may not be discharged stably, and the shielding effect from the static electricity may be reduced.